Berkeley, CA (Scicasts) — Professor George Brooks has been trying to reshape thinking about lactate - in the lab, the clinic and on the training field - for more than 40 years, and finally, it seems, people are listening. Lactate, it's becoming clear, is not a poison, it's the antidote.

In a recent article in the journal Cell Metabolism, Brooks, a professor of integrative biology at the University of California, Berkeley, reviews the history of the misunderstanding of lactate - often called lactic acid - a small molecule that plays a big role in metabolism. Typically labeled a "waste" product produced by muscles because lactate rises to high levels in the blood during extreme exercise, athletic trainers and competitive athletes think of lactate as the cause of muscle fatigue, reduced performance and pain.

Starting in the 1970s, however, Brooks, his students, postdoctoral fellows and staff were the first to show that lactate wasn't waste. It was a fuel produced by muscle cells all the time and often the preferred source of energy in the body: The brain and heart both run more efficiently and more strongly when fueled by lactate than by glucose, another fuel that circulates through the blood.

"It's a historic mistake," Brooks said. "It was thought that lactate is made in muscles when there is not enough oxygen. It has been thought to be a fatigue agent, a metabolic waste product, a metabolic poison. But the classic mistake was to note that when a cell was under stress, there was a lot of lactate, then blame it on lactate. The proper interpretation is that lactate production is a strain response, it's there to compensate for metabolic stress. It is the way cells push back on deficits in metabolism."

Gradually, physiologists, nutritionists, clinicians and sports medicine practitioners are beginning to realize that high lactate levels seen in the blood during illness or after injury, such as severe head trauma, are not a problem to get rid of, but, in contrast, a key part of the body's repair process that needs to be bolstered.

"After injury, adrenaline will activate the sympathetic nervous system and that will give rise to lactate production," Brooks said. "It is like gassing up the car before a race."

Without this added fuel, the body wouldn't have enough energy to repair itself, and Brooks says that studies suggest that lactate supplementation during illness or after injury could speed recovery. Over the course of decades of research, Brooks has discovered that there are at least three main uses of lactate in the body: It's a major fuel source, it's the major material to support blood sugar level and it's a powerful signal for metabolic adaptation to stress.

"The reason I wrote the review is that people in all these different disciplines are seeing different effects of lactate, and I am pulling it all together," said Brooks. "Lactate formulations have been used for decades to fuel athletes during prolonged exertions; it's been used widely for resuscitation after injury and to treat acidosis. Now, in clinical experiments and trials, lactate is being used to help control blood sugar after injury, to fuel the brain after brain injury, to treat inflammation and swelling, for resuscitation in pancreatitis, hepatitis and dengue infection, to fuel the heart after myocardial infarction and to manage sepsis."

Brooks's research has already benefitted endurance athletes. In 1989, he worked with a sports firm to create an energy drink called Cytomax that includes a lactate polymer that can gives athletes an energy boost before and during competition. A combination of lactate, glucose and fructose, it takes advantage of the different ways the body uses fuel: lactate can get into the blood twice as fast as glucose - peaking in just 15 compared to 30 minutes after drinking. Most sports drinks contain only glucose and fructose.

Lactate shuttle

Brooks is a physiologist who has focused on exercise and nutrition since joining the UC Berkeley faculty in 1971. He discovered that normal muscle cells produce lactate all the time, and coined the term "lactate shuttle" to describe the feedback loops by which lactate is an intermediary supporting the body's cells in many tissues and organs.

We all store energy in several forms: as glycogen, made from carbohydrates in the diet and stored in the muscles; and as fatty acids, in the form of triglycerides, stored in adipose tissue. When energy is needed, the body breaks down glycogen into lactate and glucose and adipose fat into fatty acids, all of which are distributed throughout the body through the bloodstream as general fuel. However, Brooks said, he and his lab colleagues have shown that lactate is the major fuel source.

Glucose and glycogen are metabolized through a complex series of steps that culminate in lactate. For almost a century, scientists and clinicians believed that lactate is only made when cells lack oxygen. However, using isotope tracers, first in lab animals and then in people, Brooks found that we make and use lactate all the time.

This is what he calls the lactate shuttle, where "producer" cells make lactate and the lactate is used by "consumer" cells. In muscle tissue, for example, the white, or "fast twitch," muscle cells convert glycogen and glucose into lactate and excrete it as fuel for neighboring red, or "slow twitch," muscle cells, where lactate is burned in the mitochondrial reticulum to produce the energy molecule ATP that powers muscle fibers. Brooks was the first to show that the mitochondria are an interconnected network of tubes -- a reticulum - like a plumbing system that reaches throughout the cell cytoplasm.

The lactate shuttle is also at work as working muscles release lactate that then fuels the beating heart and improves executive function in the brain.

In discovering the lactate shuttle and mitochondrial reticulum, Brooks and his UC Berkeley colleagues have revolutionized thinking about metabolic regulation in the body; not just in the body under stress, but all the time.

For decades scientists and clinicians believed that in cells, glycogen and glucose are degraded to the lactate precursor substance called pyruvate. That turned out to be wrong, since pyruvate is always converted to lactate, and in most cells lactate rapidly enters the mitochondrial reticulum and is burned. Working with lactate tracers, isolated mitochondria, cells, tissues and intact organisms, including humans, Brooks and UC colleagues discovered what had been missed and, consequently, misinterpreted. More recently, others have used magnetic resonance spectroscopy (MRS) to confirm that lactate is continuously formed in muscles and other tissues under fully aerobic (oxygenated) conditions.

Brooks notes that lactate can be a problem if not used. Conditioning in sports is all about getting the body to produce a larger mitochondrial reticulum in cells to use the lactate and thus perform better.

Tellingly, when lactate is around, as during intense activity, the muscle mitochondria burn it preferentially, and even shut out glucose and fatty acid fuels. Brooks used tracers to show that both the heart muscle and the brain prefer lactate to glucose as fuel, and run more strongly on lactate. Lactate also signals fat tissue to stop breaking down fat for fuel.

"One of the important things about lactate is that it gets into the circulation and participates in inter-organ communication," said Jen-Chywan "Wally" Wang, a UC Berkeley professor of nutritional sciences and toxicology. "Which is why it's very important in normal metabolism and an integral part of whole-body homeostasis."

Lactate is the body's VISA

In his review, Brooks emphasizes three major roles for lactate in the body: It's a major source of energy; a precursor for making more glucose in the liver, which helps support blood sugar; and a signaling molecule, circulating in the body and blood and communicating with different tissues, such as adipose tissue, and affecting the expression of genes responsible for managing stress.

For example, studies have shown that lactate increases the production of Brain-Derived Neurotropic Factor (BDNF), which in turn, supports neuron production in the brain. And, as a fuel source, lactate immediately improves the brain's executive function, whether lactate is infused or comes from exercise.

"It's like the VISA of energetics; lactate is accepted by consumer cells everywhere it goes," he said.

The fact that lactate is an all-purpose fuel makes it a problem in cancer, however, and some scientists are looking for ways to block the lactate shuttles in cancer cells to cut off their energy supplies.

"Recognition that lactate shuttles among producer and consumer cells in tumours offers the exciting possibility of reducing carcinogenesis and tumour size by blocking producer and recipient arms of lactate shuttles within and among tumour cells," he wrote in his review.

All this presages a turnaround in the appreciation of lactate, though Brooks admits that textbooks - except for his own, Exercise Physiology: Human Bioenergetics and Its Applications, now in its fourth edition - still portray lactate as a bad actor.

"Lactate is the key to what is happening with metabolism," Brooks said. "That is the revolution."

Article adapted from a University of California, Berkeley news release.

La Jolla, CA (Scicasts) — Recovery after severe spinal cord injury is notoriously fraught, with permanent paralysis often the result. In recent years, researchers have increasingly turned to stem cell-based therapies as a potential method for repairing and replacing damaged nerve cells.

They have struggled, however, to overcome numerous innate barriers, including myelin, a mixture of insulating proteins and lipids that helps speed impulses through adult nerve fibers but also inhibits neuronal growth.

But in a new paper, published in the May 23 online issue of Science Translational Medicine, researchers at University of California San Diego School of Medicine report that adult rat myelin actually stimulated axonal outgrowth in rat neural precursor cells (NPCs) and human induced pluripotent (iPSC)-derived neural stem cells (NSCs).

"It's really a remarkable finding because myelin is known to be a potent inhibitor of adult axon regeneration," said Dr. Mark Tuszynski, professor of neuroscience and director of the UC San Diego Translational Neuroscience Institute. "But that isn't the case with precursor neurons or those derived from stem cells."

Tuszynski's lab, with colleagues in Germany and Singapore, monitored neurite outgrowth from NPCs and NSCs growing on a myelin substrate in Petri dishes. Neurites are projections from the cell bodies of neurons, either axons (which carry signals outward to other neurons) or dendrites (which receive the signals). In both cases, they found outgrowth enhanced threefold.

In subsequent studies using rats with spinal cord injuries, the researchers found that rat NPCs and human iPSC-derived NSCs implanted at the injury site both extended greater numbers of axons through adult central nervous system white matter than through gray matter, and preferentially associated with rat host myelin.

Paring away some of the myelin molecules known to strongly inhibit axonal growth, Tuszynski and colleagues identified a molecule called reuronal growth regulator 1 or Negr1 as a potential mediator between axons and myelin, permitting the former's growth. Negr1 is involved in the process by which cells attach to neighboring cells and interact. The growth factor plays an important role during embryological development, when neurons are growing rapidly but before myelin begins to have an inhibitory effect.

"When we implant neural stem cells into sites of spinal cord injury, they extend tens of thousands of axons out of the injury site for distances of up to 50 millmeters," said Tuszynski. "Adult axons on the other hand, when coaxed to grow, extend 100 axons for a distance of one millimeter. These findings identify why axon outgrowth from neural stem cell implants is so much better than injured adult axons."

The findings support the developing approach of using neural precursor cells and iPSC-derived stem cells as a viable and promising method for repairing spinal cord injuries, wrote the study authors. More specifically, they point to the need to further investigate the stimulatory effects of myelin on NPCs and NSCs, which "could potentially be exploited for neural repair after spinal cord injury."

Article adapted from a University of California San Diego news release.

Aurora, CO (Scicasts) — Research by physician-scientists at the University of Colorado Anschutz Medical Campus offers hope for improved quality of life for people who rely on intravenous nutrition due to intestinal damage.

Dr. Karim C. El Kasm, assistant professor of pediatrics, and Dr. Ronald Sokol, professor of pediatrics, are authors of an article in the April 2018 Nature Communications that sheds light on the underlying cause of intestinal failure-associated liver disease and suggests new therapeutic approaches.

Intestinal failure is a condition that occurs when a person's intestines are injured, damaged, or surgically shortened resulting in the need for the person to receive daily intravenous (IV) nutrition to sustain health. This IV nutrition, called parenteral nutrition, can be given in the hospital or at home through semi-permanent IV catheters.

Side effects of this form of nutrition are jaundice, liver injury called cholestasis, and eventually scarring in the liver. Intestinal failure-associated liver disease could eventually become so severe that the person would need a liver transplant or a combined liver and intestinal transplant to survive.

Until recently, there has been no effective therapy because of a poor understanding of how intestinal failure related to the development of the liver disease. Over the past decade, investigators have learned that reducing or changing the IV lipids can have a beneficial effect on some, but not all, patients.

Drs. El Kasmi and Sokol developed a mouse model that mimics the situation in humans with intestinal failure who depend on IV nutrition. Mice with intestinal injury that are given PN through a central venous catheter for 7 to 28 days develop decreased liver function, called cholestasis, and liver injury.

The researchers were able to show that products from bacteria in the intestine of the mice, called lipopolysaccharides (LPS), are absorbed through the injured intestine and activate the immune system in the liver to produce a cytokine, IL-1 beta, leading to cholestasis. The combination of IV lipids and intestinal injury lead to the intestinal failure-associated disease.

With this understanding, the researchers identified three possible new targets for drug intervention to prevent or treat intestinal failure-associated disease. Several drugs that target these disease-causing pathways are already approved or in development. Further testing in clinical trials with affected patients is required, but this research opens the possibility of treating patients who need long-term IV nutrition without the worry of developing serious liver damage.

Article adapted from a University of Colorado Anschutz Medical Campus news release.

Philadelphia, PA (Scicasts) — Mutations to the protein tau, commonly associated with neurodegenerative disorders, may serve as a novel risk factor for cancer.

"Our study revealed that the presence of tau mutations raises the risk of developing cancer," said Dr. Fabrizio Tagliavini, scientific director, IRCCS Foundation Carlo Besta Neurological Institute, Milan, Italy. "Furthermore, our bioinformatic analysis highlighted a broader functional environment for the tau protein, which had been previously associated mainly with disease development in the context of neurodegeneration."

Tau protein is essential for the stabilization of microtubules, a major element of the eukaryotic cytoskeleton. Defective tau protein is traditionally associated with neurodegenerative disorders, such as Alzheimer's disease and frontotemporal lobar degeneration (FTLD). "A mutated tau has a reduced ability to bind to microtubules; this leads to microtubule destabilization and cytoskeleton disruption, which is detrimental to cellular survival," explained Tagliavini. "Additionally, free tau protein can form toxic aggregates within nerve cells, impairing neuronal function."

Previous work in the Tagliavini lab found that mutations in tau led to chromatin defects and chromosome abnormalities. "It is well-known that chromosome aberrations are often linked to cancer," said Tagliavini.

"Therefore, we decided to determine if there was a possible association between tau mutations and cancer."

Tagliavini and colleagues analyzed cancer incidence in 15 families bearing seven different tau mutations and affected by FTLD. To calculate cancer risk, each tau-mutated family was matched with three reference families with superimposable pedigrees (control subject's age, gender, and native location matching the person affected with FTLD).

Fifteen percent of subjects from tau-mutated families developed cancer, while only 9 percent of subjects from the reference families had cancer. Cancer types in both cohorts were variable; tau mutations were not associated with specific cancers. Following multivariate analysis, the researchers determined that individuals from tau-mutated families were 3.72 times more likely to develop cancer compared to the reference families.

The researchers also used a bioinformatics analysis to understand the interactions of tau protein with other proteins. They found that almost a third of proteins that tau interacts with were involved in DNA metabolism and cell cycle control; aberrant regulation of these key processes can lead to cancer, explained Tagliavini.

"Patients carrying tau mutations are usually attended for neurodegeneration," said Tagliavini. "However, with further confirmation of our results, these patients could also be monitored for their risk of developing cancer. Clinicians should take into account both of these aspects of tau pathology."

Limitations of the study include missing genetic analyses from several patients and individuals from reference families due to the unavailability of DNA. "The analysis of missing patient data would have allowed a more significant correlation between cancer and tau mutations, which had to be inferred with statistical analysis," noted Tagliavini.

Article adapted from a American Association for Cancer Research news release.

Munich, Germany (Scicasts) — How to install new capabilities in cells without interfering with their metabolic processes? A team from the Technical University of Munich (TUM) and the Helmholtz Zentrum München have altered mammalian cells in such a way that they formed artificial compartments in which sequestered reactions could take place, allowing the detection of cells deep in the tissue and also their manipulation with magnetic fields.

Prof. Gil Westmeyer, Professor of Molecular Imaging at TUM and head of a research team at the Helmholtz Zentrum München, and his team accomplished this by introducing into human cells the genetic information for producing bacterial proteins, so-called encapsulins, which self-assemble into nanospheres. This method enabled the researchers to create small, self-contained spaces - artificial cellular compartments - inside mammalian cells.

Protected areas with new properties

The great strength of the little spheres is that they are non-toxic to the cell and enzymatic reactions can take place inside them without disturbing the cell's metabolic processes. "One of the system's crucial advantages is that we can genetically control which proteins, for example, fluorescent proteins or enzymes, are encapsulated in the interior of the nanospheres," explains Felix Sigmund, the study's first author. "We can thus spatially separate processes and give the cells new properties."

But the nanospheres also have a natural property that is especially important to Westmeyer's team: They can take in iron atoms and process them in such a way that they remain inside the nanospheres without disrupting the cell's processes. This sequestered iron biomineralization makes the particles and also the cells magnetic. "To render cells visible and controllable remotely by making them magnetic is one of our long-term research goals. The iron-incorporating nanocompartments are helping us to take a big step towards this goal," explains Westmeyer.

Magnetic and practical

In particular, this will make it easier to observe cells using different imaging methods: Magnetic cells can also be observed in deep layers with methods that do not damage the tissue, such as Magnetic Resonance Imaging (MRI). In collaboration with Dr. Philipp Erdmann and Prof. Jürgen Plitzko from the Max Planck Institute of Biochemistry, the team could additionally show that the nanospheres are also visible in high-resolution cryo-electron microscopy. This feature makes them useful as gene reporters that can directly mark the cell identity or cell status in electron microscopy, similar to the commonly used fluorescent proteins in light microscopy. Moreover, there are even additional advantages: Cells that are magnetic can be systematically guided with the help of magnetic fields, allowing them to be sorted and separated from other cells.

Use in cell therapy conceivable

One possible future use of the artificial cellular compartments is, for example, cell immunotherapies, where immune cells are genetically modified in such a way that they can selectively destroy a patient's cancer cells. With the new nanocompartments inside the manipulated cells, the cells could in the future be possibly located easier via non-invasive imaging methods. "Using the modularly equipped nanocompartments, we might also be able to give the genetically modified cells new metabolic pathways to make them more efficient and robust," explains Westmeyer. "There are of course many obstacles that have to be overcome in preclinical models first, but the ability to genetically control modular reaction vessels in mammalian cells could be very helpful for these approaches."

Article adapted from a Technical University of Munich (TUM) news release.